Cardiac pacing methods

ABSTRACT

The described method of treatment relates to the field of cardiovascular disease and is a cure for various forms of heart fibrillation. The method consists of sectioning the heart into independent conduction zones such that electrical communication between the zones is terminated. The communication between the zones is then reestablished in such a manner as to restore normal heart rhythm, by way of a pacing mechanism, thereby eliminating the fibrillation.

The present application is a continuation-in-part of U.S. Pat. Ser. No.08/932,785, U.S. Pat. No. 5,836,985 filed Sep. 18, 1997.

FIELD OF INVENTION

The present invention relates to the field of cardiovascular disease andmore particularly, the treatment of fibrillation including but notlimited to atrial fibrillation.

BACKGROUND

Atrial fibrillation (AF) involves rapid and chaotic beating of theindividual fibers of the heart muscle such that synchronous contractionis not maintained. This inevitably results in that part of the heartceasing to pump blood, which in turn can lead to embolic stroke. Atrialfibrillation is characterized by the presence of multiple reentrantcircuits that may be active simultaneously, precluding the synchronousactivation of enough atrial myocardium to generate an identifiable pwave or coordinated atrial contraction. Either a sinus impulse or astable atrial flutter reentrant circuit (flutter wave) may degenerateinto the multiple reentrant circuits (multiple wavelets) characteristicof atrial fibrillation. [Cox et al., J. Thoracic. Cardiovas. Surg.101:402-405 (1991)].

Degeneration of the stable activation patterns of sinus rhythm andatrial flutter into atrial fibrillation is enhanced when there is adisparity in the local refractory periods of closely approximatedregions of atrial myocardium. However, atrial geometry, atrialanisotropy, and histopathologic changes in the atrial myocardium mayalso predispose to both atrial flutter and atrial fibrillation.

Atrial fibrillation currently afflicts over three million persons in theUnited States. [Cox et al., J. Thoracic. Cardiovas. Surg. 101:402-405(1991)]. It is the most common sustained arrhythmia, increasingprogressively in prevalence with advancing age, and occurring in 2%-4%of the population over the age of 60. Atrial fibrillation is associatedwith atherosclerosis, chronic rheumatic heart disease, and hypertensiveheart disease. The medical treatment of atrial fibrillation is less thanoptimal in that it frequently fails to ablate the arrhythmia and isultimately directed only toward the control of the ventricular responserate. This results in patients (1) continuing to experience theunpleasantness of an irregular heartbeat, (2) continuing to suffer theconsequence of impaired hemodynamics because of loss of atrioventricularsynchrony, and (3) remaining vulnerable to the thromboemboliccomplications of atrial fibrillation.

For example, certain antiarrhythmic drugs, like quinidine andprocainamide, can reduce both the incidence and the duration of atrialfibrillation episodes. Yet, these drugs often fail to maintain sinusrhythm in the majority of patients. Atrio-venticular nodal blockingagent, e.g. drugs, like digitalis, Beta blockers, and calcium channelblockers, can also be given to control the ventricular response.However, many people are intolerant to such drugs. [Kerr, PACE17:1203-1207 (1994)].

Nonpharmacologic tools to treat atrial fibrillation include atrialdefibrillation, catheter ablation, and open heart surgery. Whileeffective means of treatment, each possess unwanted drawbacks.

External electrical cardioversion/defibrillation has been an effectivemethod for termination of atrial fibrillation. It has been awell-accepted mode of acute therapy for over thirty years. However,there is potential risk of myocardial damage, ventriculartachyarrhythmias, or thromboembolism with this technique. [Luderitz etal., Am. J. Cardiol. 77:45A-52A (1996)]. Most importantly, the procedureonly terminates the event and does not treat the underlying problem.

Implantable atrial defibrillators have been used in patients recently.This method is accomplished by the implantation of an internaldefibrillator and a nonthoractomy lead system. However, patients withfrequent episodes of fibrillation or episodes of short duration andspontaneous termination are not good candidates and alternative methodsof treatment must be attempted. Major problems involved with theimplantation technique include the presence of continual pain, the riskof inducing ventricular tachycardia during low level shocks and rapidbattery depletion. [Luderitz et al., Am. J. Cardiol. 77:45A-52A (1996)].

Ablation of the atrioventricular node (AV node) in patients with chronicor paroxysmal atrial fibrillation has been extensively described andprovides relief in selected patients. The patient, however, is left inatrial fibrillation and therefore there is a persistent risk ofthromboembolism and continued loss of contractile atrial function. Thistechnique uses catheter ablation by radiofrequency energy to permanentlydisconnect the fibrillating atria from the ventricles. Pacing is thenpermanently provided to the ventricle. [Fritzpatrick et al., Am. HeartJ. 131(3):499-507 (1996)]. In addition, radiofrequency catheter ablationhas been used to create linear lesions in the right atrium. Thistechnique uses a specially designed 14-polar catheter and results in thepatient being free from arrhythmias or the need for medication for up to3 months. Although encouraging results were obtained, the selection ofpatients that may utilize this specialized technique are very limited.Luderitz et al., Am. J. Cardiol. 77:45A-52A (1996)].

One open heart surgical procedure is the so-called "corridor" procedure.This approach separates the fibrillating atria from a strip of tissueconnecting the sinus and the AV node. Because both right and left atriacontinue to fibrillate, the hemodynamic abnormalities associated with AFare not improved. In addition, the vulnerability to the development ofleft atrial thrombi is not alleviated. Originally, it was hypothesizedthat this small corridor of atrial tissue would not be large enough tosustain AF. However, AF may continue and anticoagulation remainsnecessary. [Luderitz et al., Am. J. Cardiol. 77:45A-52A (1996)].

Another open heart surgical procedure for treating atrial fibrillation,termed the "maze procedure", has been found to be effective in treatingatrial fibrillation. The procedure makes a prescribed pattern ofincisions to anatomically create a convoluted path, or maze, forelectrical propagation within the left and right atria. The incisionsdirect the electrical impulse from the SA node along a specified routethrough both atria, resulting in a uniform contraction and thereforenormal atrial transport function. The incisions finally direct theimpulse to the AV node to activate the ventricles, restoring normalatrioventricular synchrony. The incisions are also carefully placed tointerrupt the conduction routes of the common reentry circuits.Appropriately placed atrial incision not only (1) interrupt theconduction routes of the most common reentrant circuits, they alsodirect (2) the sinus impulse from the sinoatrial node to the AV nodealong a specified route and (3) preserve synchronous atrial electricalactivation as a prerequisite for contraction. The maze procedure hasbeen found effective in treating atrial fibrillation. Yet, despite itsclinical success, the maze procedure is technically difficult to do andrequires open heart surgery. Moreover, the procedure is not tailored toa specific patient and sometimes can result in a permanent loss ofcontractile atrial function. Because of these factors, only a few mazeprocedures are done each year. (U.S. Pat. No. 5,549,661 to Kordis etal., incorporated herein by reference).

What is needed presently is a safe method of treatment that is both costeffective and versatile enough to be used on a wide variety of cardiacdiseases. The method would improve the patient's quality of life byallowing for increased performance of everyday tasks as well asproviding a general satisfaction with overall health. In addition, itwould lower the number of visits the cardiac patient must make to theirphysician, thus reducing health care costs. Also, the mortality rate forthese patients will decline.

SUMMARY OF THE INVENTION

The present invention relates to new methods of treating cardiovasculardisease, more particularly fibrillation of the heart. In one embodiment,the method comprises the steps of a) providing: i) a subject having aheart; ii) a means for sectioning the heart; and iii) a means forstimulating the heart; b) sectioning the heart into independentconduction zones with said sectioning means; and c) stimulating theindependent conduction zones with said stimulating means.

In another embodiment, the method comprises the steps of a) providing:i) a subject having a heart, ii) a means for sectioning the heart, iii)a means for stimulating the heart, and iv) a catheter; b) introducingsaid catheter into said subject; c) introducing said sectioning meansinto said subject through said catheter; d) sectioning the heart intoindependent conduction zones with said sectioning means, and e)stimulating the independent conduction zones with said stimulatingmeans.

It is not intended that the invention be limited to subjects with anyone type of cardiac disease. Potential cardiac diseases include: atrialfibrillation (chronic or paroxymal), atrial flutter and ventricularfibrillation. Also, the age, sex, or degree of disease state is notintended to be in any way limiting to the present invention.

A preferred embodiment of the invention is sectioning of the heart byway of non-invasive means. However, it is contemplated that the creationof independent conduction zones by way of lesions may be accomplishedwith invasive as well as non-invasive surgical techniques.

In another embodiment, the heart has metal sutures placed in regions ofthe atria that need to be electrically isolated. This is performedduring either a limited thoracotomy or during a median sternotomy thatis being performed for another procedure (eg. coronary artery bypassgraft, or valve replacement/repair). The ends of the suture are taken tothe body surface, a technique that is similar to that used to taketemporary epicardial pacing wires to the body surface. Once the patienthas recuperated from the surgery, uncoupling is performed by passingeither an electric current or other energy source such that uncouplingoccurs at the metal suture-tissue interface. Once the uncoupling hastaken place, the wires are removed by gentle traction (similar to theprocedure used with the epicardial pacing wires).

In another embodiment, the heart is sectioned into independentconduction zones by way of catheter ablation. However, it is notintended that the invention be limited by any particular method ofsectioning.

In a preferred embodiment, the catheter ablation forms curvilinearlesions onto the heart. It is not intended that the invention be limitedby any particular number or configuration of lesions created byablation. Also, the invention is not limited to the precise length,width, depth, or spacing between lesions.

While it is not intended that the present invention be limited by theparticular method of catheter ablation, a preferred method is byradiofrequency. Other contemplated ablation or modification techniquesinclude but are not limited to: electrical catheter, laser, ultrasound,cryogenics, surgery, and alcohol or phenol ablation.

In another embodiment, the heart is sectioned into at least twoindependent conduction zones. In addition, the sectioning of the heartinto independent conduction zones is not intended to be limited to anyparticular chamber of the heart.

In a preferred embodiment, the means for stimulation is placed insidethe body of the subject. However, it is contemplated that the means forstimulation may be externally placed as well (just under the skin or onthe surface of the skin).

Where placed inside the body, the present invention contemplates anembodiment where the means for stimulation is attached to the surface ofthe heart (e.g. on the epicardial surface). However, it is alsocontemplated that the means for stimulation may lie in contact with theinternal lining of the heart (e.g. on the endocardial surface).

In one embodiment, the means for stimulating the independent conductionzones are implantable solid state devices. In another embodiment, themeans for stimulation is a pacemaker.

In another embodiment, the means for stimulating is comprised of atleast one electrode and a power source. Further, it is not intended thatthe electrode(s) be limited in the number, size, or spacing, theconfiguration and shape being variable.

The means for stimulating the independent conduction zones iscontemplated to be used on any chamber of the heart and should not bethought to be limited to either the left or right, or atrium orventricle, or any combination thereof. The stimulation is not intendedto be limited by its intensity, the intensity being adjusted byincreasing the number of pulses, the width of the pulses, the amplitudeof the and/or their frequency. Moreover, they may be individual or trainpulses.

In another embodiment, the means for stimulation is able toautomatically vary the stimulation depending on physiologic conditions.These conditions being a change in physical activity, mixed venousoxygen saturation, right ventricular pressure, or any other conditionscontemplated by one skilled in the art.

Definitions

The following definitions are to be used to further explain theinvention and should in no way be used to limit the scope of theinvention.

"Subject" as used herein refers to a vertebrate. Preferably, thevertebrate is a human.

"Independent conduction zones" as used herein are electrically isolatedregions created by the making of lesions within the chamber(s) of theheart.

"Catheter" as used herein refers to a device for insertion into canals,vessels, passageway or body cavities to permit recording of electrogramsand in a preferred embodiment, a catheter can be used in a catheterablation technique. "Catheter ablation" is a technique wherein lesionsare created in the heart muscle tissue by insertion of a catheterfollowed by either radiofrequency, thermal, or cavitational ablation.

"Means of sectioning" as used herein refers to a means for physicallyterminating the electrical communication between cells. In oneembodiment heart tissue is ablated by way of a medical device. In apreferred embodiment, the medical device is a catheter which emitsradiofrequency energy.

"Means for stimulating" as used herein refers to a medical device whichproduces a burst of energy either in individual or pulse trains in apredetermined or varied amount. In a preferred embodiment, a signal froma sensing system applies pacing to the independent conduction zones.

"Solid state electrical device" as used herein refers to devices whichutilize either electrical, magnetic, or photic properties of solidmaterials.

"Non-invasive" as used herein refers to the ability to enter thesubjects body without cutting into the tissues of the body. In apreferred embodiment, the non-invasive means is through a blood vessel.

"Curvilinear lesions" as used herein refers to lines of section on theinside of the heart (i.e., endocardium) such that communication from oneside of the line to the other is not possible.

"Cardiac disease" as used herein refers to a state in which the heart ofa subject is no longer able to function within normal parameters.

"Internally" as used herein refers to the state of being inside thebody.

"Automatically varies the amount of stimulation depending on physiologicconditions" as used herein refers to the pacing device changing thephase of stimulation of the various independent conduction zones suchthat the maximal cardiac output is achieved.

"Radiofrequency energy" as used herein refers to an electromagnetic wavefrequency intermediate between audio frequencies and infraredfrequencies.

"Re-establishing functional communication" as used herein refers to thepacing of independent conduction zones in a way such that there is acoordinated contraction of both the right and left atria. Conductiontherefore starts away from the AV groove and proceeds towards thisregion, therefore ejecting blood into the ventricle.

"Temporal protocol" as used herein refers to the time sequence forpacing independent conduction zones.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a diagram depicting the electrically isolated atrial sectionsof one preferred embodiment.

FIGS. 1B and 1C display two possible ways of sectioning the atrium.

FIG. 2 is an isochronal map of the atrium after sectioning which isrepresentative of one embodiment of the present invention.

FIG. 3 depicts an electrogram during pacing in the atrium proper.

FIG. 4 depicts an electrogram from the "atrium proper" where theventricles were not captured by the pacing.

FIG. 5 is an isochronal map of the atrium following electricalrecoupling of two sectioned portions of the atria which isrepresentative of one embodiment of the present invention.

FIG. 6 is a flow chart of software that controls the pacing technique ofone embodiment of the present invention.

FIG. 7 is a normal electrocardiogram.

DESCRIPTION OF THE INVENTION

The present invention provides devices and methods for control of heartfibrillation. In a preferred embodiment the present invention is used tocontrol atrial fibrillation. One proposed embodiment of the inventioncontemplates the use of non-invasive procedures for both ablation andimplantation of a pacing device which would also eliminate the morbidityand mortality associated with open-heart surgical techniques. Thepresent method of treatment is a substantial improvement over existingtechniques because it presents a potential "cure" for atrialfibrillation, and does not require defibrillation. In one preferredembodiment, a subject with a diseased heart is treated by sectioning theheart into independent conduction zones by catheter ablation, followedby stimulating the independent conduction zones with a heart pacingdevice.

Subjects of which the present method of treatment is proposed to cureinclude those with the following known cardiac diseases: atrialfibrillation, ventricular fibrillation, ventricular tachycardia andcomplete or partial atrioventricular block. However, it is not intendedthat the present method be limited to only the above proposed cardiacdiseases. It is also not intended that the invention be limited as to aparticular subject. A subject as described in the definition sectionrefers to a vertebrate, preferably a human.

I. Heart Function

The operation of the heart is regulated by electrical signals producedby the heart's sino-atrial (SA) node. Each signal produced by the SAnode spreads across the atria and ventricles of the heart, depolarizingthe muscle fibers as it spreads. Atrial and ventricular contractionsoccur as the signal passes. After contracting, the myocardial cellsrepolarize during a short period of time, returning to their restingstate. Once repolarized, the muscle cells are ready to be depolarizedagain by a signal from the SA node.

At rest, the normal adult SA node produces a signal approximately 60 to85 times a minute, causing the heart muscle to contract, and therebypumping blood to the remainder of the body. This constitutes therepetitive, cyclic behavior of the heart. Each cycle in the operation ofthe heart is called a cardiac cycle.

Atrial geometry, atrial anisotropy, and histopathologic changes in theleft or right atria can, alone or together, form anatomical obstacles.The obstacles can disrupt the normally uniform propagation of electricalimpulses in the atria. These anatomical obstacles (called "conductionblocks") can cause the electrical impulse to degenerate into severalcircular wavelets that circulate about the obstacles. These wavelets,called "reentry circuits," disrupt the normally uniform activation ofthe left and right atria. Abnormal, irregular heart rhythm calledarrhythmia, results. This form of arrhythmia is called atrialfibrillation, which is a very prevalent form of arrhythmia.

To analyze the heart's operation, a variety of techniques have beendeveloped for collecting and interpreting data concerning the electricalactivity of the heart. One of the most basic of these approaches is theelectrocardiograph (ECG). As an electrical signal spreads across theheart, which we shall call an electrical wave front, an ECG repetitivelymeasures the voltages at various electrodes relative to a designated"ground" electrode. The ECG typically plots each lead over an intervalof time such that the heart's electrical activity for one or morecardiac cycles is displayed for purposes of monitoring or analysis. Thethree most common ECG's are known as the "12 lead", the "18 lead," andthe vector cardiograph.

A cardiac cycle as measured by the ECG is partitioned into three mainelements which reflect the electrical and mechanical operation of theheart. The portion of a cardiac cycle representing atrial depolarizationis referred to as a "P-wave." Depolarization of the ventricular musclefibers is represented by "Q", "R", and "S" points of a cardiac cycle.Collectively these "QRS" points are called an "R-wave" or a "QRScomplex." The portion of a cardiac cycle representing repolarization ofthe ventricular muscle fibers is known as a "T-wave." It is through theuse of an ECG that one is able to determine whether fibrillation is oris not occurring and allows one to manipulate the heart tissue toprovide treatment.

II. Independent Conduction Zones

One embodiment of the invention provides a method of treatment whereinthe atrium or ventricle is sectioned into distinct independentconduction zones (ICZ) electrically isolated from each other. In oneembodiment, the ICZs are created by non-invasive interventions such asradiofrequency, thermal or cavitational ablation. In an alternativeembodiment, it is contemplated that localized drug or gene delivery maybe used to anatomically or functionally uncouple the electricalconnection between the cells.

One aspect of the invention provides a method of ablating tissue in theheart to treat atrial fibrillation by introducing into a selected atriuma sectioning means, such as an elongated energy emitting element thatcan be flexed along its length from a generally straight shape into avariety of curvilinear shapes. The proposed method exposes the catheterinto a desired shape. The method applies ablating energy to or throughthe catheter to destroy tissue, forming an elongated lesion having acontour that follows the flexure of the catheter. The method is thenrepeated with tissue exposure, catheter flexing and energy applicationsteps being provided at different spaced regions along the atrial wall.In this way, a convoluted lesion pattern comprising elongated straightlesions and elongated curvilinear lesions is produced. This electricaluncoupling interrupts the reentry circuits thereby preventing atrialfibrillation

In a preferred embodiment, the method introduces the catheter through avascular approach, without opening the heart. In this embodiment, themethod applies radiofrequency electromagnetic energy to ablate thetissue. The working catheter segments contemplated are typically about 6French to 8 French in diameter and with a sheath member approximately7-10 French in diameter.

In one proposed embodiment, functional communication between the cellswould be reestablished through the use of implantable solid statedevices (ISSD) in each ICZ, which communicate with each other in acontrolled way so as to establish a temporal protocol for stimulatingeach ICZ.

In a preferred embodiment, these ISSDs would be implanted usingnoninvasive, catheter-based techniques. In one embodiment, the ISSDswill utilize microcircuit technology to incorporate a sensing element, apacing element, a computing element and a power element.

This procedure will essentially establish a distributed pacing systemeither under control of a master pacing device implanted under the skin,or under natural cardiac control (sino-atrial or atrio-ventricular node)with appropriate sensors in the ISSDs. Communication within the ICZswill be by normal cell-to-cell coupling and between the ICZs by theISSDs.

III. Pacemakers

A pacemaker maintains the heart rate of a patient between a certainprogrammable range. For example, in humans that range is typicallybetween 60-80 beats per minute (lower rate) and 120-160 beats per minute(upper rate). As noted above, in one embodiment, the present inventioncontemplates a pacemaker as a means for stimulating the independentconduction zones and reestablishing functional communication between thezones. A pacemaker automatically applies a pacing impulse to the heartof sufficient magnitude to depolarize the tissue. The device is adaptedto continue delivering intermittent pacing to the heart in the eventthat the heart fails to return to its normal behavioral pattern, and hasthe ability of automatically regaining sensing control over a functionalheart, thereby insuring that further pacing is inhibited.

The pacemaker circuit comprises two basic subsystems; a sensing system,which continuously monitors heart activity; and a stimulation systemwhich upon receiving a signal from the sensing system applies a pacingimpulse to the myocardium through an intravascular electrical lead. Afirst bipolar lead is coupled to the pulse generator and has anelectrode located at its distal end to sense and pace the atrium. Asecond bipolar lead coupled to the generator is used for sensing andpacing the ventricle. A circuit is provided for applying impedancemeasuring current pulses between one of these electrodes and the other.

In one embodiment, an off the shelf pacemaker capable of both atrial andventricular pacing/sensing is used. The specific pacemakers preferredfor this purpose include a Medtronic Thera, a Medtronic Elite 2 (bothmade by Medtronic, Inc. Minneapolis, Minn.), or Pacesetter TrilogyDR+(Pacesetter, a St. Jude's company, Minneapolis, Minn.) as these havea minimum programmable delay between atrial and ventricular pacing of 40msec. To effectuate pacing according to one embodiment of the invention,both the leads from the atrial and the ventricular segment of thepacemaker are connected to the atrium. To allow more than one segment tobe paced per lead, a bifurcation system can be used. Such leads arecommercially available and can be used as an off the shelf product. TheY-adapter (for example CPI MODEL #6835, or #6024, made by CardiacPacemakers Inc., Minneapolis, Minn.) would allow one of the sockets fromthe pacemaker (atrial or ventricular) to then be bifurcated to twoleads. Therefore, each output would then be able to pace twoelectrically isolated segments of the atrium. For epicardial pacing, CPImodel #4312 lead (Cardiac Pacemakers Inc., Minneapolis, Minn.) can beused and this has a 4.75 mm pin. For endocardial pacing, CPI model #4161(Cardiac Pacemakers Inc., Minneapolis, Minn.) could be used. In thismanner, a standard dual chamber pacemaker could be used to pace fourICZ's.

A. Sensing Elements Of A Pacemaker

In a standard dual chambered pacemaker, the sensing circuits monitoractivity both in the atrium and ventricle. If a sensed event occurs inthe atrium, this initiates a ventricular paced event if no ventricularactivity occurs during the programmed atrioventricular delay. If nosensing occurs in the atrium or ventricle, pacing is initiated tomaintain the programmed lower rate.

When the pacemaker device is used for the present invention, similarsensing algorithms will be useful in the appropriate pacing of thevarious ICZs. It is particularly desirable that the pacemaker include asensor of a physiologic parameter related to demand for cardiac output,such as an activity sensor, a respiration sensor or an oxygen saturationsensor. Various dual chamber pacing devices have incorporated some formof sensor to provide a physiologic pacing rate. Similar sensing iscontemplated for the present invention to maintain a physiologic rate.

B. Pacing Elements

In a standard dual chamber pacemaker, pacing of both atrium andventricle is possible. In the current invention, pacing of the variouselements will take place once requested by the sensing algorithm. Thestandard burst generator pacemaker employs appropriate technology forthe generation of stimulation pulses in the form of individual pulses orpulse trains having an amplitude up to 7 V and a pulse width of up to 1msec. Most pacemakers have these parameters as a programmable option.The pacing rate is also programmable in most pacemakers and the range isbetween 35-160 beats/min.

Given that the circuitry for pulse generation has become well known tothose skilled in the art, no detailed disclosure is included herein.Specific timing, amplitude, duration and the number of pulses iscontrolled by a microprocessor via data bus under the control of aprogram stored in memory.

C. Computing Elements And Software

The computing element is a microprocessor which operates as an interruptdriven device, and is awakened by interrupts from pacer timing/controlcircuitry corresponding to the occurrence of sensed R-waves andcorresponding to the generation of cardiac pacing pulses. Theseinterrupts are provided via data/address bus. Any necessary mathematicalcalculations will be performed by the microprocessor and any updating ofthe values or intervals controlled by pacer timing/control circuitrytake place following such interrupts.

D. Power Elements

Any form of implantable stimulating device must be powered by aportable, depletable power source, such as a battery. When the batteryis depleted of its energy, it is necessary to explant the device andimplant a replacement. As a result, for an implantable device to beconsidered commercially viable, it is generally believed that the deviceshould have a predicted lifetime of a number of years, such as fiveyears, which is contemplated for the proposed device.

While the stimulating device is described in the form of amicroprocessor based programmable stimulator, the method of treatmentincorporating the device is sufficiently simple that the stimulatingdevice could readily be embodied in the form of a full custom digitalintegrated circuit based device or even a device employing analog timingunits. Therefore, the above disclosure should be considered explanatory,rather than limiting with regard to what is claimed.

Experimental

The following example serves to illustrate certain preferred embodimentsand aspects of the present invention and is not to be construed aslimiting the scope thereof.

In the experimental disclosure which follows, the followingabbreviations apply: kHZ (kilo-hertz); SA (sinoatrial); AV(atrioventricular); msec (millisecond); QRS ("Q", "R", and "S" points ofa cardiac cycle); and ECG (electrocardiogram).

EXAMPLE 1

Using an open chest canine preparation, a portion of the atrium wassectioned into three electrically isolated regions as depicted in FIG.1A. Linear lesions were produced using a radionics 300 kHz,approximately 40-50 watt radiofrequency generator [Radionics Inc.,Burlington, Mass.] in two dogs. In a third dog, the lesions were made bycutting the atrium with a scalpel after clamping the relevant portion ofthe tissue to control bleeding.

Electrical isolation of the segments was documented both by high densityelectrode mapping using the CardioMAP equipment [Prucka Engineering,Houston, Tex.] as depicted in FIG. 2 and also by pacing maneuvers. FIG.2 displays an isochronal map of the atrium during sinus rhythm, afterthe sectioning procedures were preformed. FIGS. 3 and 4 are examplesdemonstrating electrical uncoupling with pacing. FIG. 1A depicts theisolation of the right atrial appendage and the medial segment of theatrium with similar mapping and pacing techniques.

A system for establishing normal atrial activity after sectioning wasdeveloped on a personal computer (PC) equipped with two digital analogboards. These two boards had two A-D (digital to analog) outputs each.(DT3001 and DT2821, Data Translations, Inc.) The Hewlett Packard HPVEEwas used to pace the isolated segments of atria in addition to the rightand left atrium. Coordinated contractile atrial function was documentedvisually and by measuring the pressure in the right atrium using a SwanGanz catheter [Abbott Critical Care Systems, North Chicago, Ill.].

The experiments demonstrate complete electrical isolation of a segmentof atria. In addition, they show that both electrical and contractileatrial function can be achieved through the use of an external PC drivensoftware program.

FIG. 1A illustrates the ablated sections of the atrium (10). Thesections include: the right atrial appendage (20), atria proper (30),which is the area including the SA node (70), the AV node (30); the leftatrial appendage (40), the medial section (50), which is the centralregion of the right atrium, and AV groove (60).

FIG. 2 displays a isochronal map of the atrium following sectioning ofthe tissue. The upper left portion of the map shows the earliestactivation and corresponds to the SA node activity. The center and lowerright regions correspond to the medial section which is electricallysilent ("ES") since it is isolated from the SA node. The activation canbe seen spreading around the region of isolation in a counter clockwisedirection, to the region on the bottom center which corresponds roughlyto the AV node.

FIG. 3 illustrates an electrogram during pacing in the "atrium proper".Line A is the limb lead, Line B is an electrogram from the medialsegment of the sectioned atrium, and Line C is from a distal portion ofthe atrium proper. During pacing the "atrium proper" at a cycle lengthof 200 msec., there is a normal conduction to the ventricle as the QRScomplexes on the surface EKG occur every 200 msec. No electricalactivity is noted from the medial segment of the sectioned atria,however, far-field ventricular activity is noted. The electrograms fromthe distal portion of the atria proper show local activation occurringapproximately 80 msec after pacing. This 80 msec is the conduction timefrom the pacing site to the recording site.

FIG. 4 illustrates an electrogram during pacing in the atrium proper asdescribed above, however, the ventricles were not captured by the pacingand were being paced by the SA node at a cycle length of approximately380 msec. Local atrial activity is noted following the pacing stimulusonly in the medial segment of the atrium (Lines A, B and C are asdescribed for FIG. 3, above).

FIG. 5 illustrates an isochronal map following recoupling of twoisolated portions of the atria. The white portions (W) denoted on themap represent areas that are not electrically active. It should be notedthat the mapping array is not of an identical position to before theablation procedure as depicted in FIG. 2.

EXAMPLE 2

Once the atrium has been sectioned into electrically isolated regionsthis results in the termination of atrial fibrillation. This has beendemonstrated in previous studies for example the maze procedure by Cox.The next step comprises the attachment of either a solid state device ora pacing lead to the center of these isolated segments. Anotherpossibility would be to first place these leads or solid state devicesat regions of the heart that require pacing and then perform sectioningto isolate these regions from each other.

An advantage of this is that, once the sectioning has been performed,one is able to demonstrate electrical isolation as seen in the exampleabove. A locator signal (either radiofrequency on ultrasound) can beemitted from the tip of the lead or the solid state device and thishelps in the three dimensional localization of the solid state device asthe lesions are made.

The exact shape and location of the electric isolated segments can bepatient specific. What is required to terminate a fibrillation is toreduce the surface area of the connected portions of the atrium. Theelectrically isolated segments need not be connected to one another forthis invention. FIG. 1B and 1C displays two possible ways of sectioningthe atrium (where "X" represents the pacing device and the independentconduction zones are shown as 1-5).

The pacing leads can then be connected to the pacing device to establishcommunication between themselves and the control device such that pacingof the various sections is then possible. The exact timing of theindependent conduction zones can be optimized for the specific patientusing the Swan Ganz recording in the right atrium and also the pulmonarycapillary wedge pressure recording (a marker of left atrial pressure).The flow chart (FIG. 6) describes the schematic view that will be usedto optimize the timing of pacing of the independent conduction zones.

In this example, four independent conduction zones (ICZ's) are assumed.Pacing of the ICZ's is performed in sequence starting off with pacingone followed by two, three, and then four with a 10 msec. delay betweeneach pacing site. Different sequence of pacing is performed and witheach sequence, measurements of mean pulmonary wedge pressure and meanright atrial pressures are taken.

The ICZ sequence that results in the largest mean RA and mean pulmonarycapillary wedge pressure is chosen for that particular patient. Thispacing sequence is then used as the optimal pacing sequence.

The algorithm need not go through every iteration as pacing the highersegments first would be more beneficial, therefore this will limit thenumber of iterations required for the measurement.

EXAMPLE 3

This example describes an alternative pacing method. In this embodiment,the exact timing of the independent conduction zones can be optimizedfor the specific patient using the measurement of the P wave durationand amplitude. This technique has an advantage over the Swan-Ganztechnique in that it is non-invasive and can be performed during aclinic evaluation.

The flow chart of FIG. 6 is again applicable. The timing of pacing ofthe independent conduction zones is optimized by achieving the narrowestP wave duration and greatest P wave amplitude. Again, pacing of theICZ's is performed in sequence starting off with pacing one followed bytwo, three, and then four with a 10 msec. delay between each pacingsite. A different sequence of pacing is performed and with eachsequence, a measurement of the P wave duration is taken.

FIG. 7 shows a normal electrocardiogram (provided herein as areference). The first deflection, P, is due to excitation of the atria.The QRS deflections are due to excitation (depolarization) of theventricles. The measurements can be either on signal average of 20 to200 PQRS complexes or can be on an individual beat by beat basis. Theadvantage of signal averaging is that the signal to noise ratio isincreased and therefore makes the measurement more accurate.

The ICZ sequence that results in the narrowest (i.e. shortest) P waveduration and the greatest P wave amplitude is chosen for that particularpatient. This pacing sequence is then used as the optimal pacingsequence.

The algorithm need not go through every iteration as pacing the highersegments first would be more beneficial, therefore this will limit thenumber of iterations required for the measurement.

From the above it is clear that the present invention provides a methodof treating irregular atrial or ventricular activity that is both costeffective and versatile. The method will improve the patient's qualityof life by allowing for increased performance of everyday tasks as wellas providing a general satisfaction with overall health. The method oftreatment will also lower the number of visits the cardiac patient mustmake to their health care provider which in turn will reduce theiroverall health care costs. Any further improvements and modificationswhich become apparent to persons of ordinary skill in the art only afterreading this disclosure, the drawings and the following claims aredeemed within the spirit and scope of the present invention.

We claim:
 1. A method, comprising the steps of:a) providing:i) a subject whose heart has been sectioned into independent conduction zones, thereby defining a plurality of isolated segments, ii) a means for stimulating said heart, said means comprising a plurality of pacing leads; and iii) a P wave measuring means; b) attaching a pacing lead to each of said isolated segments; c) stimulating said independent conduction zones with said stimulating means, said stimulating comprising stimulating each of said independent conduction zones in series to define a phase of stimulation; and d) measuring, with said P wave measuring means, the P wave generated by said stimulating of step c); e) changing said phase of stimulation of said independent conduction zones; and f) repeating steps c), d) and e) until the narrowest P wave duration and the greatest P wave amplitude is measured, thereby providing coordinated contraction of both the right and left atria of said heart of said subject.
 2. The method of claim 1, wherein said heart is sectioned into at least four independent conduction zones.
 3. The method of claim 1, wherein said means for stimulating said heart comprises at least one electrode and a power source.
 4. The method of claim 1, wherein said means for stimulating are solid state electrical devices.
 5. The method of claim 1, wherein said means for stimulating is a pacemaker.
 6. A method, comprising the steps of:a) providing:i) a means for stimulating said heart, said means comprising a plurality of pacing leads; ii) a subject whose heart has been sectioned into independent conduction zones, thereby defining a plurality of isolated segments, each of said segments attached to said stimulating means via said pacing leads; and iii) a P wave measuring means; b) stimulating said independent conduction zones with said stimulating means, said stimulating comprising stimulating each of said independent conduction zones in series to define a phase of stimulation; and c) measuring, with said P wave measuring means, the P wave generated by said stimulating of step b); d) changing said phase of stimulation of said independent conduction zones; and e) repeating steps b), c), and d) until the narrowest P wave duration and the greatest P wave amplitude is measured, thereby providing coordinated contraction of both the right and left atria of said heart of said subject.
 7. The method of claim 6, wherein said heart is sectioned into at least four independent conduction zones.
 8. The method of claim 6, wherein said means for stimulating said heart comprises at least one electrode and a power source.
 9. The method of claim 6, wherein said means for stimulating are solid state electrical devices.
 10. The method of claim 6, wherein said means for stimulating is a pacemaker.
 11. A method, comprising the steps of:a) providing:i) a means for stimulating said heart, said means comprising a plurality of pacing leads; ii) a subject whose heart has been sectioned into independent conduction zones, thereby defining a plurality of isolated segments, each of said segments attached to said stimulating means via said pacing leads; and iii) a pressure measuring means; b) stimulating said independent conduction zones with said stimulating means, said stimulating comprising stimulating each of said independent conduction zones in series to define a phase of stimulation; and c) measuring, with said pressure measuring means, the mean pulmonary wedge pressure and mean right atrial pressure of said heart of said subject generated by said stimulating of step b); d) changing said phase of stimulation of said independent conduction zones; and e) repeating steps b), c), and d) until the largest mean right atrial and mean pulmonary capillary wedge pressure is measured, thereby providing coordinated contraction of both the right and left atria of said heart of said subject.
 12. The method of claim 11, wherein said heart is sectioned into at least four independent conduction zones.
 13. The method of claim 11, wherein said means for stimulating said heart comprises at least one electrode and a power source.
 14. The method of claim 11, wherein said means for stimulating are solid state electrical devices.
 15. The method of claim 11, wherein said means for stimulating is a pacemaker. 